To produce structured elements having a three-dimensional surface structure, it is known to machine the surface to be structured of the workpiece used to produce the element with focused laser radiation. If the workpiece consists of a workpiece material transparent to the laser radiation used, then laser-induced ablation is possible if operations are carried out in the area of multi-photon absorption (non-linear absorption).
For example, machining a workpiece from the front side with an ultra-short-pulse laser is known. The laser beam is focused onto the entry-side surface of the workpiece. Although the workpiece is transparent to the laser wavelength used (e.g. in the visible or NIR range), the focusing produces such a high intensity that ablation takes place at the workpiece surface as a result of multi-photon absorption. It is possible for only specific structures to be produced. For example, the wall angles of the removal are restricted by the parameters of the optical structure. Any desired steep angles cannot be produced even with tracking of the focus. In addition, for example, no structures with undercuts can be produced.
“Subsurface precision machining of glass substrates by innovative lasers” by K. Du and P. Shi in: Glass Sci. Technol. 76 (2003) No. 2 describes, amongst other things, a technique permitting precise hollow structures to be produced in glass, which would be impossible with conventional mechanical methods. It is also possible, otherwise than in the front-side process, for example, to produce structures with undercuts and a high aspect ratio. In the method, the laser beam from a nanosecond laser is radiated into the glass from the upper side and is focused on the opposite underside. It is possible for the evaporated glass material to freely flow away from the machining zone. By suitable deflection of the beam, it is possible to produce precise and reproducible holes with any desired cross section in the glass.
Laser-induced backside wet etching (LIBWE) is a method of introducing microstructures directly and with high quality into transparent dielectric materials. The etching process takes place on the rear side of the transparent sample, which is in contact with an absorbent liquid.
DE 19912879 A1 describes a method of etching a transparent substance with a pulsed laser beam, in which the side of the material opposite the laser-irradiated surface and in contact with a fluid absorbing the laser radiation is removed by absorption of the laser radiation by the fluid. The fluid claimed is a bath of a solution or dispersion of organic substances and inorganic pigments.
DE 102005055174 B3 describes a method of material removal by laser radiation of materials transparent to the laser wavelength by applying pulsed laser radiation to the side of the transparent material opposite with respect to the incident laser radiation and in contact with a liquid having a high absorption coefficient of greater than 1000 cm−1 in the spectral range 0.2 to 11 μm, wherein the liquid has metallic properties.
It could be helpful to provide a generic method of producing a structured element permitting structured elements with very fine and cleanly defined three-dimensional surface structures to be created, and to provide a device that performs the method and also correspondingly produces structured elements.